Abuse, good memories. It's one of the games (other being StarCraft and Unreal Tournament) which pushed me into learning programming as a kid. Funny that after 10 years I suddenly remembered that I had my first Lisp exposure over a decade before I learned about the language itself - it was by browsing Abuse data files.
https://en.wikipedia.org/wiki/Abuse_(video_game)
http://lispgames.org/index.php/Abuse
Although, from the FAQ:
http://abuse.zoy.org/wiki/doc/faq
"Approximately seven percent of the game engine and Abuse combined is Lisp code. The rest is C++."